Just happened to take a gander at the Economy tab of my Govern window. I'm in a random Small map game, originally with 3 enemies (I have streamrolled two of them so far), and because I wanted to tech up farther, rather than just win early, I beat the last AI down to one city and then let them beg me for peace.

So, as a result of that demolishing I did, the third AI (Resoln) is making negative Gildar (aka losing money aka negative cash flow). They decided to give me tribute (I really hate how offered tribute is still called a "Demand" from me in game), with some up front. But the economy tab shows me making -.4 G per turn from their "tribute". Which means I'm being tributed 10% of their "earnings" of -3.9 G/turn... which is costing me money.